Various techniques to be used for face image recognition by a computer have been proposed. For example, a technique for performing the facial recognition by executing the principal component analysis to collected face images is described in Non-patent Literature 1.
Meanwhile, techniques have been proposed for generating various images of an object in cases where the direction of the object and the illumination are changed. In a technique described in Non-patent Literature 2, images of an object in cases where the direction and the illumination are changed are generated by measuring the three-dimensional shape of the object. When an image is generated from the three-dimensional shape, the position and posture of the three-dimensional shape are adjusted so that the difference in the degree of similarly to a target image decreases.
In a technique described in Non-patent Literature 3, a three-dimensional shape of an object is measured previously. An image approximate to the target image is generated from the three-dimensional shape of the object. The matching a two-dimensional image of the object in which the illumination/posture condition is unknown with the image approximate to the target image is performed.
When a two-dimensional image is generated from the three-dimensional shape of each object, positioning and adjusting posture is performed so that the difference in the degree of similarly to the target image decreases. In this process, the position and posture of the three-dimensional shape are adjusted so that parts where the difference from the target image is large are hidden. Consequently, the image is generated using only areas of the three-dimensional shape where the difference from the target image is small. Thus, the generated image tends to be small.
Patent Literature 1 and Non-patent Literature 4 describe methods for the calculation of the degree of similarly between face images. In the methods, the degree of similarly of each area in the images is calculated, the degrees of similarly are integrated after each weight is given to each degree of similarly, and a integrated degree of similarly is used.
Non-patent Literature 5 describes a technique for generating an image in which edge parts have been detected in an image.
Non-patent Literature 6 describes a technique for acquiring three-dimensional shape data of an object.
Non-patent Literature 7 describes a technique for estimating the posture (direction) of a three-dimensional face model that matches a face image.
Patent Literature 2 describes an image matching device which generates the base vectors of illumination variation space by performing the principal component analysis and generates an image approximate to an input image from the base vectors.
Non-patent Literature 8 describes a technique for determining hidden areas, where the face is hidden by other objects, in a face image.